(1) Field of the Invention
The present invention relates to image-forming apparatus such as copying machines and laser beam printers having constructions similar to the copying machines which, after forming an image on recording paper inside their machine body, are capable of selective discharge of the recording paper, either face down, i.e. with an image-carrying side down, or face up, i.e. with the image-carrying side up.
(2) Description of the Prior Art
Some image-forming apparatus for forming images on recording paper in response to image information, such as laser beam printers, copying machines, facsimile equipment, and printing machines, are constructed to selectively discharge the recording paper face down or face up for convenience of the operator in recording operations.
FIG. 4 shows, in sectional front view, an outline of one such image-forming apparatus known in the art, which is a laser beam printer 50 here.
The illustrated laser beam printer 50 comprises a machine body 60 housing a photoreceptor drum 61 rotatable clockwise in a substantially central position thereof. The drum 61 is surrounded by a main charger 62, a developer 63, a transfer charger 64 and a cleaning device 65.
The drum 61 is exposed by a laser beam modulated by an image signal and deflected by a polygonal mirror 66.
A paper feed tray 67 is mounted to the righthand side of the machine body 60. A feed roller 68 takes recording paper P sheet by sheet from the tray 67, and feeds the paper P to a transport passage including a timing roller pair 69, a conveyer belt 70 and fixing rollers 71. While advancing through this passage, the recording paper P receives an image from the drum 61 and has the image fixed thereto by the fixing rollers 71.
The paper P carrying the image fixed thereto is discharged either through a face-down discharge passage to a face-down tray 76 provided on top of the machine body 60 or through a face-up discharge passage to a face-up tray 77 removably attached to the machine body 60. As seen, the face-down discharge passage extends from the fixing rollers 71 through a guide 80, passage walls 74 and a face-down discharge roller pair 72. The face-up discharge passage extends from the fixing rollers 71 through the guide 80 and a face-up discharge roller pair 73.
The guide 80, face-down discharge roller pair 72, passage walls 74 and face-up discharge roller pair 73 constituting the discharge passages are all disposed inside the machine body 60. The guide 80 is pivotable by operating a lever not shown, for selecting between the two discharge passages.
FIG. 4 shows a state in which the face-down discharge passage is selected. In this state, the recording paper P carrying an image formed on an upper side thereof is turned over while passing through the passage walls 74, and discharged with the image-carrying side facing down.
The face-down discharge results in the sheets of recording paper P arranged in the order of image formation. This advantageously dispenses with an operation for rearranging the sheets, i.e. putting the sheets in the order of page numbering, after the image-forming operation.
For this reason, the face-down discharge is used in most cases with printers such as the laser beam printer 50 which discharges sheets one page after another.
On the other hand, the face-up discharge with the face-up tray 77 attached to the machine body 6 enables the operator to look at the image immediately upon discharge of the recording paper P. This has the advantage of allowing the image-forming operation to be carried out while confirming the formed image. Compared with the face-down discharge, the face-up discharge has the further advantage of paper transport reliability with little chance of paper jamming since its passage extends substantially straight and does not include a curve such as defined by the passage walls 74. Thus, the face-up discharge is selected particularly when using thick paper such as envelopes.
In order to meet various operational requirements or user needs, the known image-forming apparatus, or the laser beam printer in this case, has the machine body 60 containing all of the guide 80 for selecting between the face-down and face-up discharge passages, the face-down discharge roller pair 72, passage walls 74 and face-up discharge roller pair 73 as noted above. The user has only to attach the face-up tray 77 for selecting either the face-down discharge or face-up discharge.
However, the face-up discharge roller pair 73 and face-up tray 77 are altogether unnecessary to the user who selects the face-down discharge in his or her day-to-day operations. Although the face-up tray 77 may be removed from the machine body 60, the face-up discharge roller pair 73 mounted in the machine body 60 is inseparable therefrom.
The machine body 60, which is the larger for containing the face-up discharge roller pair 73 used rarely, allows a reduced working space for the user. There is also a disadvantage of the machine body 60 being costly with the inclusion of the face-up discharge roller pair 73.